The present invention generally relates to asynchronous transfer mode (ATM) networks and, more particularly, to ATM networks and methods for efficiently combining and transmitting information from multiple end users.
ATM is a fast packet/cell switching technology used to transmit voice, data, image, and video signals. All broadband transmissions, whether audio, data or video, are divided into a series of fixed length cells and routed across an ATM network connected by ATM switches.
ATM technology is a connection-oriented protocol based on a standard 53-byte cell. The first five bytes carry control information and are referred to as the xe2x80x9cheaderxe2x80x9d of the ATM cell. The remaining 48 bytes carry user information or data. A virtual connection (VC) between end users must be set up before the end users can send information to each other. This is in contrast to a connectionless-oriented protocol, wherein a temporary virtual connection is established on demand when information is to be transferred.
Two of the key elements in the header of the ATM cell are known as the xe2x80x9cVirtual Path Identifierxe2x80x9d and the xe2x80x9cVirtual Circuit Identifier.xe2x80x9d These are abbreviated as VPI and VCI, respectively. The VPI or VPI/VCI together xe2x80x9cidentifyxe2x80x9d an ATM cell (i.e., the address of a cell), and determine the xe2x80x9croutingxe2x80x9d of the cell within an ATM switch or a router. For additional information on ATM technology and details of how these fields are used to uniquely identify a cell as well as how they are used to route a cell in a switch or router, see the ITU-T or ATM Forum Standards.
ATM networks typically do not allow simultaneous transmission of high bandwidth information in a multipoint-to-multipoint two-way connection. This restricts the use of ATM networks in applications where several users would like to send and receive, simultaneously, video, image or data information and compare and contrast such information. For example, medical technology applications include situations where transmitters of information are located in different parts of the world, and receivers of information desire to compare/contrast images and video signals in real time.
Various attempts have been made to increase the amount of information which can be transmitted on a VC. Up to this point, implementations encompass the idea of a xe2x80x9cframe mergexe2x80x9d, which interleaves traffic from different users at the frame level (rather than at the cell level). To implement a frame-merge, an ATM switch at the merge point stores incoming cells until an entire packet has arrived within the switch. The switch will then send the entire packet to the merged VC, while at the same time preventing any other user from transmitting information on the same merged VC. This approach has several disadvantages, including sophisticated channel control design requirements, extensive hardware resource requirements (e.g., buffers in the ATM switches), and the failure of this type of xe2x80x9cstore and forwardxe2x80x9d approach to carry real-time traffic. The frame-merge approach is simply impractical for real-time transmission of multimedia data over a label-switched Internet Protocol (IP) network.
Therefore, there is a need for a traffic merging network and method of operating a network that provides for merging information at less than the frame level. However, to be practical, this need must be solved by a network and method which are supported by current ATM switch hardware. Such a network and method will allow transition from current practices to the more efficient approach even before a specific operating standard is implemented. Such an approach will have many advantages over the hardware-based frame-merge solution.
Accordingly, the present invention provides an asynchronous transfer mode (ATM) network comprising a multiplicity of source stations, wherein each one of the source stations is identified by a source identifier (SID) and is connected to at least one non merged virtual channel (VC); a first ATM switch having a first input, a second input, and an output, such that the first input is connected to one of the non-merged virtual channels (VCs), the second input is connected to a different one of the non-merged VCs, and the output is connected to a merged VC; and at least one destination station connected to the merged VC, which maintains a SID allocation table containing each one of the source identifiers (SIDs).
The ATM network may make use of SIDs that are unique, bidirectional, and/or non-dedicated. One embodiment of the present invention may utilize no more than a single bidirectional SID.
The ATM network may further comprise the assignment of virtual channel identifiers (VCIs) to each of the source stations and into which the respective SIDs are inserted for identification of individual cell data. Another possible means of identifying the data cells is to insert the SID into a virtual path identifier (VPI) which is assigned to each one of the non-merged VCs.
The ATM network operates by having one of the source stations transmit a first data cell to a first ATM switch, and having a different source station transmit a second data cell to the first ATM switch; the first ATM switch is then used to transmit the first and second data cells to the destination station via the merged VC. The ATM network may also be constructed such that a second ATM switch is interposed between the first ATM switch and the destination station.
The present invention further provides an ATM network comprising a first and second source station, wherein the first source station is identified by a first source identifier (SID) and connected to a first non-merged VC. The ATM network also comprises a second source station which is connected to a second non-merged VC and is identified by a second SID, the first SID being different from the second SID. The ATM network also comprises a first ATM switch having a first input, a second input, and an output, such that the first input is connected to the first non-merged VC, the second input is connected to the second non-merged VC, and the output is connected to a merged VC. The ATM network further comprises a destination station connected to the merged VC; the destination station maintains a SID allocation table which contains the first and second source identifiers (SIDs). The SID allocation table may contain one or more bidirectional SIDs, and/or at least one non-dedicated SID.
This embodiment of the present invention may also contain virtual channel identifiers (VCIs) which are assigned to the first and second source stations, wherein the first SID is inserted into the VCI assigned to the first source station, and wherein the second SID is inserted into the VCI assigned to the second source station. The SIDs may also be inserted into virtual path identifiers (VPIs) which are assigned to the non-merged VCs.
This alternative embodiment of the ATM network may comprise the use of the first source station to transmit a first data cell to the first ATM switch, and the use of the second source station to transmit a second data cell to the first ATM switch, and the use of the first ATM switch to transmit the first and second data cells to the destination station via the merged VC. This embodiment of the present invention may also comprise a network in which a second ATM switch is interposed between the first ATM switch and the destination station.
Further, the present invention provides a method of operating an ATM network comprising the steps of receiving a first user data cell at a source station connected to a non-merged VC, assigning a unique SID to the source station, transmitting the first data cell to a first ATM switch via the first non-merged VC, receiving a second user data cell at a second source station connected to a second non-merged VC, assigning a unique SID to the second source station, transmitting the second data cell to the first ATM switch via the second non-merged VC, and transmitting the first and second data cells to a destination station via the merged VC.
The method of operating an ATM network may also comprise the step of inserting a unique SID into a virtual channel identifier (VCI), most preferably within the first and second assigning steps. Further, the method of operating an ATM network may be used when a second ATM switch is interposed between a first ATM switch and the destination station. The method of operating an ATM network may also comprise the step of separating the first and second data cells received from the merged VC using a SID allocation table maintained by the destination station. The SID allocation table may also contain a bidirectional SID, or a non-dedicated SID.
One advantage of the present invention is that data cells are still scheduled and queued in the same manner as is commonly effected by present hardware designs.
Another advantage of the present invention is that the ATM network and method of operation sort all ATM traffic classes, both during real-time and non-real-time data transmission.
A further advantage of the present invention is to allow user data cells from different source stations to share the same virtual channel connection and still be identifiable when they are received as merged data cells at the destination station.
Yet another advantage of the present invention is a significant reduction in the number of virtual channels required to transmit information in a label-switched Internet Protocol (IP) network, which in turn increases the scalability of label-switching technology.